5 research outputs found
Transition phenomena in unstably stratified turbulent flows
We study experimentally and theoretically transition phenomena caused by the
external forcing from Rayleigh-Benard convection with the large-scale
circulation (LSC) to the limiting regime of unstably stratified turbulent flow
without LSC whereby the temperature field behaves like a passive scalar. In the
experiments we use the Rayleigh-B\'enard apparatus with an additional source of
turbulence produced by two oscillating grids located nearby the side walls of
the chamber. When the frequency of the grid oscillations is larger than 2 Hz,
the large-scale circulation (LSC) in turbulent convection is destroyed, and the
destruction of the LSC is accompanied by a strong change of the mean
temperature distribution. However, in all regimes of the unstably stratified
turbulent flow the ratio varies slightly (even in the range
of parameters whereby the behaviour of the temperature field is different from
that of the passive scalar). Here are the integral scales of
turbulence along x, y, z directions, T and \theta are the mean and fluctuating
parts of the fluid temperature. At all frequencies of the grid oscillations we
have detected the long-term nonlinear oscillations of the mean temperature. The
theoretical predictions based on the budget equations for turbulent kinetic
energy, turbulent temperature fluctuations and turbulent heat flux, are in
agreement with the experimental results.Comment: 14 pages, 14 figures, REVTEX4-1, revised versio
Effect of large-scale coherent structures on turbulent convection
We study an effect of large-scale coherent structures on global properties of
turbulent convection in laboratory experiments in air flow in a rectangular
chamber with aspect ratios and (with the Rayleigh
numbers varying in the range from to ). The large-scale
coherent structures comprise the one-cell and two-cell flow patterns. We found
that a main contribution to the turbulence kinetic energy production in
turbulent convection with large-scale coherent structures is due to the
non-uniform large-scale motions. Turbulence in large Rayleigh number convection
with coherent structures is produced by shear, rather than by buoyancy. We
determined the scalings of global parameters (e.g., the production and
dissipation of turbulent kinetic energy, the turbulent velocity and integral
turbulent scale, the large-scale shear, etc.) of turbulent convection versus
the temperature difference between the bottom and the top walls of the chamber.
These scalings are in an agreement with our theoretical predictions. We
demonstrated that the degree of inhomogeneity of the turbulent convection with
large-scale coherent structures is small.Comment: 10 pages, 12 figures, REVTEX
Evidence for somatic translocation during potato dihaploid induction
Potato dihaploid PDH55 (Solatium tuberosum) is exclusively euploid (2n = 24) but apparently contains and expresses DNA from dihaploid inducer IVP48 (S. phureja). Genomic in situ hybridization (GISH) suggested IVP48 DNA incorporated stably into PDH55 by somatic translocation. This finding has two important implications. Firstly, the long-held implicit assumption that euploid dihaploids produced by dihaploid inducers are pure S. tuberosum seems incorrect. This may complicate meiotic, genetical and molecular studies involving potato dihaploids. Secondly, if such translocations are not rare, the phenomenon may offer a novel way to introduce useful traits directly from wild dihaploid-inducing species into S. tuberosum. © 1995 The Genetical Society of Great Britain